This invention relates to an apparatus for transmitting energy to and from superconductive coils, or for transmitting the energy stored in one coil to another coil through a capacitor.
FIG. 1 illustrates a conventional apparatus of this type as disclosed in Ueda et al, "Energy Transfer Experiment With Flying Capacitor Circuit" Superconductor Energy Storage Oct. 10, 1979 (p118-121). In FIG. 1, the apparatus comprises a capacitor 1 for transmitting energy, an energy releasing coil 31, an energy absorbing superconductive coil 41, and thyristor elements 11-14.
The operation of this apparatus follows a method of transmitting energy wherein, after transmitting the energy stored in the coil 31 to the capacitor 1 little by little, the energy from the capacitor 1 is transmitted to the coil 41. FIG. 3 indicates this transmission order. The sequential operation 1-4 shown in FIG. 3 constitute one cycle, whereas FIGS. 2(a)-(c) show the voltage changes in the capacitor 1 and coils 31, 41 in an operating section between operations 1-4. FIG. 2 illustrates the voltage Vc across the terminals of the capacitor 1, the voltage V1 across the terminals of the coil 31, and the voltage V2 across the terminals of the coil 41.
In FIG. 1, because the on and off states of the thyristors 11-14 are established according to the voltage polarity of the capacitor 1, the voltage polarity of the capacitor 1 is always inverted at the point of time of the termination of the operation 3 shown in FIG. 3. Moreover, because the terminal voltage of the capacitor 1 is provided with a polarity such as is incapable of biasing the thyristor 12 in the reverse direction, the thyristor 12 may not be voluntarily turned on and this makes quick-response control impossible.
The quantity of energy that can be transmitted per unit time when the currents in the superconductive coils are equal is given by ##EQU1## where I.sub.1 =current of the coil 31, .DELTA.T=the maximum on time of the thyristor 13 and Vc.sub.Max =the maximum voltage of the capacitor 1.
The conventional apparatus thus constructed has the following disadvantages:
(a) The apparatus requires a bipolar capacitor for transmitting purposes. PA1 (b) The capacitance value of the capacitor cannot be made greater from the standpoint of the relation between the inductance value of the coil and the energy transmitting speed. PA1 (c) The apparatus is lacking in rapid-response controllability because the time factor makes control impossible in view of circuit operation. PA1 (d) Since the terminal voltage applied to the energy transmitting coil is in the shape of a ramp, the quantity of energy that can be transmitted is small in comparison with the maximum value of the coil voltage.